Support cross-compiling AArch64 FIPS to Android.

In order to support cross-compiling:
  1) inject-hash needs to know to use SHA-256 for the hash function
     on Android. Since that's a good idea on Aarch64 in general
     (due to common hardware support), do it for all Aarch64.
  2) We need to use the compiler to run the preprocessor, not plain
     cpp, because the compiler will get the built-in #defines right.

Change-Id: Ie00d46e9e6d489fcb9e3f3e5e625aa289c7e0d73
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/45044
Reviewed-by: David Benjamin <davidben@google.com>

crypto/fipsmodule/CMakeLists.txt

diff --git a/crypto/fipsmodule/CMakeLists.txt b/crypto/fipsmodule/CMakeLists.txt
index b74d50c..83cf3f7 100644
--- a/crypto/fipsmodule/CMakeLists.txt
+++ b/crypto/fipsmodule/CMakeLists.txt
@@ -125,9 +125,14 @@
 perlasm(x86-mont.${ASM_EXT} bn/asm/x86-mont.pl)
 
 function(cpreprocess dest src)
+  set(TARGET "")
+  if(CMAKE_ASM_COMPILER_TARGET)
+    set(TARGET "--target=${CMAKE_ASM_COMPILER_TARGET}")
+  endif()
+
   add_custom_command(
     OUTPUT ${dest}
-    COMMAND cpp ${src} -I${PROJECT_SOURCE_DIR}/include > ${dest}
+    COMMAND ${CMAKE_ASM_COMPILER} ${TARGET} $CMAKE_ASM_FLAGS -E ${src} -I${PROJECT_SOURCE_DIR}/include > ${dest}
     DEPENDS
     ${src}
     ${PROJECT_SOURCE_DIR}/include/openssl/arm_arch.h
@@ -193,11 +198,16 @@
   set_target_properties(bcm_hashunset PROPERTIES POSITION_INDEPENDENT_CODE ON)
   set_target_properties(bcm_hashunset PROPERTIES LINKER_LANGUAGE C)
 
+  set(MAYBE_INJECT_HASH_SHA256_FLAG "")
+  if (ARCH STREQUAL "aarch64")
+    set(MAYBE_INJECT_HASH_SHA256_FLAG "-sha256")
+  endif()
+
   go_executable(inject_hash
 	        boringssl.googlesource.com/boringssl/util/fipstools/inject_hash)
   add_custom_command(
     OUTPUT bcm.o
-    COMMAND ./inject_hash -o bcm.o -in-archive $<TARGET_FILE:bcm_hashunset>
+    COMMAND ./inject_hash -o bcm.o -in-archive $<TARGET_FILE:bcm_hashunset> ${MAYBE_INJECT_HASH_SHA256_FLAG}
     DEPENDS bcm_hashunset inject_hash
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
   )

crypto/fipsmodule/bcm.c

diff --git a/crypto/fipsmodule/bcm.c b/crypto/fipsmodule/bcm.c
index 083e2df..601c4a8 100644
--- a/crypto/fipsmodule/bcm.c
+++ b/crypto/fipsmodule/bcm.c
@@ -195,7 +195,7 @@
   assert_within(rodata_start, kP256Params, rodata_end);
   assert_within(rodata_start, kPKCS1SigPrefixes, rodata_end);
 
-#if defined(OPENSSL_ANDROID)
+#if defined(OPENSSL_AARCH64) || defined(OPENSSL_ANDROID)
   uint8_t result[SHA256_DIGEST_LENGTH];
   const EVP_MD *const kHashFunction = EVP_sha256();
 #else